Diamond is a preferred material for electronic devices because it has semiconductor properties that are better than traditionally used silicon (Si), germanium (Ge) or gallium arsenide (GaAs). Diamond provides a higher energy band gap, a higher breakdown voltage and a greater saturation velocity than these traditional semiconductor materials. These properties of diamond yield a substantial increase in projected cutoff frequency and maximum operating voltage compared to devices fabricated using Si, Ge, or GaAs. Si is typically not used at temperatures higher than about 200.degree. C. and GaAs is not typically used above 300.degree. C. These temperature limitations are caused, in part, because of the relatively small energy band gaps for Si (1.12 eV at ambient temperature) and GaAs (1.42 eV at ambient temperature). Diamond, in contrast, has a large band gap of 5.47 eV at ambient temperature, and is thermally stable up to about 1400.degree. C.
Diamond is also a preferred material for mechanical devices. Diamond is chemically inert and has high strength properties. Diamond has the highest thermal conductivity of any solid at room temperature and exhibits good thermal conductivity over a wide temperature range. The high thermal conductivity of diamond may be advantageously used to remove waste heat from an integrated circuit, particularly as integration densities increase. Diamond is also electrically insulating. In addition, diamond has a smaller neutron cross-section which reduces its degradation in radioactive environments, i.e., diamond is a "radiation-hard" material.
Because of the advantages of diamond as a material for electronic and mechanical devices, there is at present an interest in the processing of diamond. For example, diamond-based devices depending on the improved mechanical properties of diamond (e.g., detectors and sensors) have been proposed, in Applications of Diamond Films and Related Materials, Elsevier Science Publishers, 1991, pp. 311-319. Diamond-based devices depending on the improved electrical properties of diamond (e.g., transistors and thermistors) have been proposed, for example in U.S. Pat. Nos. 4,806,900 to Fujimori et al., 5,099,296 to Mort et al. and 5,066,938 to Kobashi et al. Many of these mechanical and electrical devices, however, require that the diamond surface be substantially smooth, and are preferably polished. Any inherent surface roughness can result in difficulty in patterning, in controlling the thickness of specific layers, and in fabricating devices.
The various current methods for polishing diamond have limitations. For example, mechanical polishing such as described in U.S. Pat. No. 4,643,161 to Kim, is sometimes difficult to control, and the resulting polished diamond layers often do not have a controlled thickness. Polishing by reaction with oxygen ion or gas often results in pitting. Various other techniques such as diffusion removal of carbon onto foil, laser ablation, argon ion-beam irradiation, hot metal lapping and electrical discharge have been used. These techniques also are sometimes difficult to control and result in diamond layers not having a controlled thickness. See, for example, Massive Thinning of Diamond Films by a Diffusion Process, Jin et al., Appl. Physics Letters, Vol. 60, No. 16, 1948 (1992); Development and Performance of a Diamond Film Polishing Apparatus With Hot Metals, Yoshikawa, SPIE Diamond Optics III, Vol. 1325, 210 (1990); and The Polishing of Polycrystalline Diamond Films, Harker et al., SPIE Vol. 1325 Diamond Optics III, Vol. 1325, 222 (1990).